This is what the Internet is:
The internet is the wider network that allows computer networks around the world run by companies, governments, universities and other organisations to talk to one another. The result is a mass of cables, computers, data centres, routers, servers, repeaters, satellites and wifi towers that allows digital information to travel around the world.
The Internet is a network of networks. Much of what people believe the Internet is actually runs on top of it: the Web, social media, email, gopher, what have you.People often say “I liked the Internet when..”. They are talking about the platforms they use on the Internet. Things popular on the Internet now — hello Facebook! — will be a relic in the future. Technologies running on the Internet come and often go, but the Internet itself is relatively constant and changes slowly.
The quote highlighted above is from this article: What is the internet? 13 key questions answered | Technology | The Guardian. It’s a good introduction to the Internet at a basic level.